"I for one am not sure why."
Because this is not for five years, but for maybe 300, and these kids, and their grandchildren are more likely to be affected by it than anybody over the age of twenty.
Despite the demonisation of the young many of them have demonstrated that they have thought long and hard about this, and many of them still are.
As for ex-pats voting, I left my native Wales in 1953. Can any body seriously suggest that I should have a say in the future of those Welsh children about to start school in September?